Our world is presently confronted with several very formidable problems, including an energy situation in which projections have been made of less than 50 remaining years of proven reserves of crude oil; increasing global temperatures that have resulted in glaciers melting and oceans rising, as well as severe climatic changes that seem to be accelerating in recent decades; and, perhaps the most foreboding problem of all, that known global reserves of phosphate rock are being rapidly depleted such that within a century global supplies will be exhausted. Phosphorus is an absolutely essential element for both plant and animal life, and the primary source of concentrated phosphorus is phosphate rock which is a non-renewable resource. Its depletion will have devastating effects, vastly reducing agricultural productivity and potentially causing massive global starvation of the projected 9.3 billion people that will inhabit the earth by 2050. Such predictions are reminiscent of those made concerning the global depletion of fixed nitrogen sources in the early 20th century. This problem was abated by the development of the Haber-Bosch process which converted diatomic nitrogen into ammonia. A parallel solution for phosphorus, however, does not exist, and recycling phosphorus from a variety of materials will be the only alternative. One further significant environmental problem associated with phosphorus is that since the end of World War II, massive quantities of phosphate have been applied to agricultural fields, golf courses, and lawns. Excess phosphate that is not incorporated into growing terrestrial plants eventually finds its way into rivers, lakes, aquifers and oceans. Under proper growing conditions, e.g., sunlight and nutrients including phosphate, microalgae can grow at very high rates, literally doubling their biomass in a matter of a few hours. They die and their decomposition consumes great quantities of oxygen resulting in fish kills and so-called “dead zones,” even in very large bodies of water such as the Gulf of Mexico.
Since ancient times, manures have been utilized as fuels for heating and cooking as well as fertilizers for enriching agricultural soils. Obvious problems associated with such practices include the odious and odorous natures of these materials, as well as the presence of disease-causing pathogens. Prior to the mid 20th century, an additional very practical issue was the lack of large collection sites, with human sewages largely being discharged into private septic systems, and animal manures produced on relatively small family farms being disposed of by application back onto fields. Those situations have changed such that, with a growing urban population, municipal waste treatment facilities have become commonplace, and small family farms have given way to very large farms, often operated by corporations, that generally specialize in production of one domestic farm animal. As a result, confined animal feeding operations (CAFOs) have emerged that accrue very large quantities of animal manures. For the most part, these manures are currently applied back onto farm fields, but in an effort to circumvent environmental problems, the quantities applied are typically restricted by regulations that are intended to control levels of nitrogen and phosphorus nutrients. This has caused large farming operations to transport wet manures significant distances from the generating farm for application onto fields having greater latitudes in terms of nutrient restrictions. As well as causing very significant odor and disease problems for local populations in the vicinity the CAFO, manures have become very significant waste products having a negative commercial value to the CAFO producer.
Phosphorus levels in agricultural fertilizers have been characterized in phosphorus pentoxide equivalents, and values for several manures produced at CAFO and municipal waste processing facilities for operations within the United States are indicated in Table 1.
TABLE 1Phosphorus capture potential for given animals per company/facility.P2O5HerdEquivalentsProductionAnnualNumber of USper day inCapacity perProductionAnimalAnimalskg/animalday (Kg)Capacity (Kg)Feeding50,0000.0683,4001,241,000PigDairy 9,3150.1501,397509,996CattlePoultry 12.9 million0.1001.29 million470 million(LayingHens)Human &226.4 million0.29165.9 million24.0 billion MunicipalWastes
Consideration of whether phosphorus in sufficient quantity could be obtained from manure sources to alleviate a global shortage problem can be ascertained from the last entry in Table 1 of output from municipal waste treatment facilities. Phosphate rock has a phosphorus pentoxide equivalence of 0.33. At the present global annual application rate of 140 million metric tons of phosphate rock (46.2 million metric tons of phosphorus pentoxide), the output from the US municipal waste treatment facilities would provide 52% of the global requirement. The precise numbers of large swine, cattle, and poultry CAFOs are unknown, but conceivably an amount of phosphorus pentoxide equivalent to the amount from the municipal waste facilities could be obtained from those sources as well. Phosphoric acid has a phosphorus pentoxide equivalent of 0.70, with dehydrated derivatives being even higher. These materials can offer better volume efficiency for long term storage.
Therefore, there is an unmet need for technologies to sequester phosphorus in the near term for use in the future.